Expression vectors for the production of recombinant proteins have existed since at least the mid 1980s. Typically, vector-based strategies for recombinant protein expression have largely been employed in basic research and for small-scale experimentation where the absolute purity of a protein preparation is not critical. In contrast, when recombinant proteins are used for therapeutic applications, even minor contaminants, for example, the presence of mis-spliced or intron read-through by-products can diminish the activity and yield of the resultant therapeutic proteins. Administration of therapeutic proteins having mis-spliced or read-through protein sequences to patients may increase the possibility of undesirable side effects.
Such by-products are also troublesome for manufacturing. The presence of by-products can compromise the purification process because such by-products are typically similar to the desired proteins in terms of size, affinity, or bioactivity. Still further, it has been observed that scaling up protein expression using recombinant host cells typically results in increasing amounts of by-products as compared to the desired product, particularly if the cells are cultured under less than optimal cell culture conditions. Such sub-optimal cell culture conditions frequently occur in large scale protein production, for example, at the end of a biofermenter run or when, for other reasons, where the health of the large scale culture deteriorates.
Accordingly, there exists a need for methods for improving recombinant protein production, particularly, for the large-scale production of therapeutic proteins.